1. Field of the Invention
The present invention relates to a photosensitive member having a plurality of amorphous silicon layers and a process for producing the same, and more particularly to a photosensitive member comprising three regions and having an amorphous silicon-germanium layer in the uppermost region and also to a process for producing the same.
2. Description of the Related Art
In recent years, many attempts have been made to use amorphous silicon (hereinafter referred to as "a-Si"), amorphous germanium or amorphous silicon-germanium (hereinafter referred to as "a-Si:Ge") for electrophotographic photosensitive members, and remarkable progress has been made in the application of such material.
As compared with a-Si, a-Si:Ge in particular is smaller in optical band gap, therefore absorbs light of long wavelengths more effectively and consequently permits generation of more carriers to exhibit an improved sensitivity to light of long wavelengths. a-Si:Ge is accordingly a promising material for use in photosensitive members for printers to which semiconductor lasers are applied. Since the material has a good sensitivity at short wavelengths, it is also applicable to PPC when the spectrum of light of the exposure lamp is adjusted. Although conventional a-Si photosensitive members often produce disturbed images due to the interference of light, the material further has the excellent feature of being less prone to this drawback because the a-Si:Ge layer satisfactorily absorbs light of long wavelengths.
Unexamined Japanese Patent Publication SHO 57-115552, for example, discloses a photosensitive member which comprises an a-Si layer on a substrate, a thin a-Si:Ge layer over the layer and a thin a-Si layer over the a-Si:Ge layer. However, this photosensitive member has difficulty in preventing injection of charges from the substrate and is not chargeable to the desired surface potential. Additionally, the carriers are not easily transportable to result in an insufficient sensitivity. U.S. Pat. No. 4,451,546 proposes a photosensitive member which comprises an a-Si semiconductor layer, an a-Si:Ge photoconductive layer and an a-Si photoconductive layer formed on an electrically conductive substrate one over another. With this member, it is necessary to enable the carriers to move efficiently toward the substrate because of the presence of the a-Si:Ge photoconductive layer in the vicinity of the outermost surface, whereas there is the problem that the carriers will be trapped by the a-Si semiconductor layer in the course of their movement.
On the other hand, it is already known to employ a glow discharge decomposition apparatus for producing photosensitive members with use of a-Si, amorphous germanium (a-Ge) or a-Si:Ge. For example, the above-mentioned U.S. patent discloses a process comprising forming the a-Si semiconductor layer on the substrate by glow discharge, then interrupting the discharge and thereafter forming the a-Si:Ge layer by resuming glow discharge and supplying the required material gases. In this case, however, the a-Si semiconductor layer differs from the a-Si:Ge layer in growth mechanism and composition, so that if the a-Si:Ge layer is formed over the a-Si semiconductor layer, separation occurs at the interface. Separation similarly occurs when the a-Si layer contains a relatively large amount of another element, e.g. carbon, and the a-Si layer to be formed thereon is free from carbon.